Astronomy:2 Ceti

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Short description: Star in the constellation Cetus
2 Ceti
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cetus
Right ascension  00h 03m 44.38784s[1]
Declination −17° 20′ 09.5719″[1]
Apparent magnitude (V) 4.483[2]
Characteristics
Spectral type B9 IVn[3]
U−B color index −0.12[4]
B−V color index −0.047±0.003[5]
Astrometry
Radial velocity (Rv)+8.0±4.6[6] km/s
Proper motion (μ) RA: +25.17[1] mas/yr
Dec.: −9.16[1] mas/yr
Parallax (π)11.98 ± 0.26[1] mas
Distance272 ± 6 ly
(83 ± 2 pc)
Absolute magnitude (MV)−0.06[5]
Details
Mass2.68±0.11[7] M☉
Radius2.75[7] R☉
Luminosity119+6
−5[8] L☉
Surface gravity (log g)3.99±0.09[7] cgs
Temperature11,419±388[9] K
Metallicity [Fe/H]+0.00±0.24[3] dex
Rotational velocity (v sin i)116[8] or 237[10] km/s
Age217[9] Myr
Other designations
Hydor, 2 Cet, BD−18°6417, FK5 905, HD 225132, HIP 301, HR 9098, SAO 147059[11]
Database references
SIMBADdata

2 Ceti, also named Hydor,[12] is a single[13] star in the equatorial constellation of Cetus, near the border with Aquarius. It is visible to the naked eye with an apparent visual magnitude of 4.483.[2] The distance to 2 Ceti can be estimated from its annual parallax shift of 12.0 mas,[1] which yields a value of around 272 light years. It appears to be moving further from the Earth with a heliocentric radial velocity of about +8 km/s.[6]

The stellar classification for this star is B9 IVn,[3] matching a B-type subgiant star with "nebulous" absorption lines due to rapid rotation.[14] Estimates of the rotation rate range from 116[8] to 237[10] km/s, and this high rate of spin is giving the star an equatorial bulge that is 12% larger than the polar radius.[14] 2 Ceti is about 217[9] million years old with 2.7[7] times the mass of the Sun and 2.75[7] times the Sun's radius. It is radiating 119[8] times the Sun's luminosity from its photosphere at an effective temperature of 11,419 K.[9] An infrared excess has been detected around this star by the Akari satellite at a wavelength of 18μm, suggesting there is an orbiting debris disk.[15]

Naming

The ancient Greek term Hydor (ὕδωρ), meaning water, originally referred to a constellation of faint stars in the region of Aquarius and Cetus.[16] The IAU Working Group on Star Names approved the name Hydor for this star on 25 August 2025 and it is now so entered in the IAU Catalog of Star Names;[12] it had previously been used for λ Aquarii, which has other cultural names.[16]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 Høg, E. et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27–L30. Bibcode: 2000A&A...355L..27H. 
  3. ↑ 3.0 3.1 3.2 Wu, Yue et al. (2010). "Coudé-feed stellar spectral library – atmospheric parameters". Astronomy & Astrophysics 525: A71. doi:10.1051/0004-6361/201015014. Bibcode: 2011A&A...525A..71W. 
  4. ↑ Nicolet, B. (1964). "Catalogue of homogeneous data in the UBV photoelectric photometric system". Astronomy and Astrophysics Supplement Series 34: 1–49. Bibcode: 1978A&AS...34....1N. 
  5. ↑ 5.0 5.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  6. ↑ 6.0 6.1 Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759–771. doi:10.1134/S1063773706110065. Bibcode: 2006AstL...32..759G. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: masses, radii and effective temperatures". Astronomy and Astrophysics 352: 555–562. Bibcode: 1999A&A...352..555A. 
  8. ↑ 8.0 8.1 8.2 8.3 Zorec, J. et al. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics 537: A120. doi:10.1051/0004-6361/201117691. Bibcode: 2012A&A...537A.120Z. 
  9. ↑ 9.0 9.1 9.2 9.3 David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal 804 (2): 146. doi:10.1088/0004-637X/804/2/146. Bibcode: 2015ApJ...804..146D. 
  10. ↑ 10.0 10.1 Royer, F. et al. (2007). "Rotational velocities of A-type stars". Astronomy and Astrophysics 463 (2): 671. doi:10.1051/0004-6361:20065224. Bibcode: 2007A&A...463..671R. 
  11. ↑ "2 Cet". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=2+Cet. 
  12. ↑ 12.0 12.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/. 
  13. ↑ Chini, R. et al. (2012). "A spectroscopic survey on the multiplicity of high-mass stars". Monthly Notices of the Royal Astronomical Society 424 (3): 1925–1929. doi:10.1111/j.1365-2966.2012.21317.x. Bibcode: 2012MNRAS.424.1925C. 
  14. ↑ 14.0 14.1 van Belle, Gerard T. (March 2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review 20 (1): 51. doi:10.1007/s00159-012-0051-2. Bibcode: 2012A&ARv..20...51V. 
  15. ↑ Ishihara, Daisuke et al. (May 2017). "Faint warm debris disks around nearby bright stars explored by AKARI and IRSF". Astronomy & Astrophysics 601: 18. doi:10.1051/0004-6361/201526215. A72. Bibcode: 2017A&A...601A..72I. 
  16. ↑ 16.0 16.1 "Hydor". IAU Working Group on Star Names. https://xing.fmi.uni-jena.de/mediawiki/index.php/Hydor. 



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